X-ray radiator with thermionic emission of electrons from a laser-irradiated cathode

Abstract

An x-ray radiator has a vacuum housing that can rotate around an axis, a cathode that thermionically emits electrons upon irradiation thereof by a laser beam, an anode that emits x-rays upon being struck by the electrons, an insulator that is part of the vacuum housing and that separates the cathode from the anode, electrodes or terminals to apply a high voltage between the anode and the cathode to accelerate the emitted electrons toward the anode to form an electron beam, a drive arrangement for rotation of the vacuum housing around its axis, an arrangement for cooling components of the x-ray radiator, and an arrangement that directs and focuses the laser beam from a stationary source that is arranged outside of the vacuum housing onto a spatially stationary laser focal spot on the cathode.

1. An x-ray radiator comprising:
 an evacuated housing mounted for rotation around an axis; 
 a cathode disposed in said housing; 
 a laser source that emits a laser beam from a stationary location outside of said vacuum housing onto a spatially stationary laser focal spot on said cathode, said laser source emitting said laser beam with a laser power that heats said cathode to cause said cathode to thermionically emit electrons; 
 an anode disposed in said housing on which said electrons are incident that emits x-rays upon being struck by said electrons; 
 an insulator forming a part of said vacuum housing that separates said cathode from said anode; 
 terminals for application of voltage between said anode and said cathode to accelerate said electrons from said cathode toward said anode as an electron beam; 
 a drive in driving engagement with said housing to rotate said housing around said axis; and 
 a cooling arrangement in thermal communication with at least one of said anode, said cathode and said housing to conduct heat therefrom. 
 
   
   
     2. An x-ray radiator as claimed in  claim 1  wherein at least one of said anode and said cathode is axially symmetric. 
   
   
     3. An x-ray radiator as claimed in  claim 1  wherein said anode exhibits a discrete axial symmetry such that rotation of said anode around said axis by an angle that is a whole-number divisor of 360° results in an identical view of the anode. 
   
   
     4. An x-ray radiator as claimed in  claim 1  wherein said cathode exhibits a discrete axial symmetry such that rotation of said cathode around said axis by an angle that is a whole-number divisor of 360° results in an identical view of the cathode. 
   
   
     5. An x-ray radiator as claimed in  claim 1  wherein said laser source generates an asymmetrically deformed laser beam that produces, as said laser focal spot on said cathode, an asymmetrical laser focal spot on said cathode. 
   
   
     6. An x-ray radiator as claimed in  claim 1  wherein said laser source includes an optical splitter that splits said laser beam into at least two sub-beams, said at least two sub-beams forming respective portions of said laser focal spot on said cathode. 
   
   
     7. An x-ray radiator as claimed in  claim 1  wherein said laser source comprises a laser beam emitter selected from the group consisting of a laser diode and a solid-state laser. 
   
   
     8. An x-ray radiator as claimed in  claim 1  wherein said laser source comprises at least one component that varies a characteristic of said laser beam selected from the group consisting of beam shape, beam intensity, and a time structure of said beam. 
   
   
     9. An x-ray radiator as claimed in  claim 1  comprising a heating arrangement that preheats a surface of said cathode, on which said laser focal spot is incident, to allow a reduced-power laser beam to cause thermionic emission of said electrons at said surface of said cathode, said heating arrangement being selected from the group consisting of electrical heating arrangements, optical heating arrangements, and inductive heating arrangements. 
   
   
     10. An x-ray radiator as claimed in  claim 1  wherein said cathode comprises a support layer, and a surface attached to said support layer on which said laser focal spot is incident. 
   
   
     11. An x-ray radiator as claimed in  claim 10  wherein said support layer has a lower heat conductivity than said surface. 
   
   
     12. An x-ray radiator as claimed in  claim 10  wherein said support layer has lower heat capacity than said surface. 
   
   
     13. An x-ray radiator as claimed in  claim 10  wherein said support layer has a lower density than said surface. 
   
   
     14. An x-ray radiator as claimed in  claim 1  comprising a magnet system that generates a magnetic field between said cathode and said anode, that interacts with said electron beam to shape and deflect said electron beam. 
   
   
     15. An x-ray radiator as claimed in  claim 1  comprising an electrode system that generates an electrostatic field between said cathode and said anode, that interacts with said electron beam to shape and deflect said electron beam. 
   
   
     16. An x-ray radiator as claimed in  claim 1  wherein said housing is a cylinder that is symmetrically supported around said axis. 
   
   
     17. An x-ray radiator as claimed in  claim 16  wherein said cathode forms a first base of said cylinder and said anode is disposed at a second, opposite base of said cylinder. 
   
   
     18. An x-ray radiator as claimed in  claim 1  wherein said cathode is a circular ring. 
   
   
     19. An x-ray radiator as claimed in  claim 1  wherein said anode is a circular ring. 
   
   
     20. An x-ray radiator as claimed in  claim 1  wherein said cathode has a cathode surface on which said laser focal spot is incident, and a support layer to which said cathode surface is attached, and wherein said laser beam source is situated relative to said cathode so that said laser beam passes through said support layer of said cathode to strike said surface. 
   
   
     21. An x-ray radiator as claimed in  claim 1  wherein said housing has an optically transparent window through which said laser beam passes to reach said cathode. 
   
   
     22. An x-ray radiator as claimed in  claim 1  comprising a radiator housing in which said evacuated housing is rotatably mounted, and wherein said cooling arrangement includes coolant circulating in said radiator housing. 
   
   
     23. An x-ray radiator as claimed in  claim 1  wherein said housing comprises heat conducting components that transport heat from at least one of said cathode and said anode inside said housing to an exterior surface of said housing.